Isoprene concentrates



L. B. PAGE ET AL 2,768,224

PROCESS FORSEPARATING PIPERYLENE AND ISOPRENE CONCENTRATES Oct. 23, 1956Filed Jan. 2, 1955 mh Ezmozoo uzmimmmi 555028 mzmmmofi ll' 1" mohzotoqfi $13 on G L I 2 0 a a m L vw i l' km L T Q mobiotoqmm L 4 LL I55cm \LEMI m Al. V A N 60.52335 mutwmm BE N5 LVO 1 15.? 55 2 2 mi 13221:nven'tors B3 5% att g United States Patent PROCESS FOR SEPARATINGPIPERYLENE ISOPRENE CONCENTRATES Leon B. Page and James W. Rector, BatonRouge, La., assignors to Esso Research and Engineering Company, acorporation of Delaware Application January 2, 1953, Serial No. 329,3463 Claims. (Cl. 260-6815) This invention relates to the treatment ofhighly cracked hydrocarbon mixtures containing mainly alkenes and dienesin the C4 to C12 range to effect a separation of an isoprene concentrateand of a piperylene concentrate freed of other dienes.

The recovery of the isoprene and piperylene concentrates separately isbeneficial for any subsequent purification, such as extractivedistillation. By the recovery method of the present invention, wherein acertain sequence of fractionation under selected conditions is used,higher isoprene recovery and improved operability of equipment areobtained. Less opportunity is given for undesired polymerization whichfouls equipment; and with lowered fouling better yields are obtained-ofthe separated dienes as monomers. The method allows an increase inhandling capacity of equipment.

The preferred sequence of operation involves the following iour steps:

(1) Heat soaking to dimerize cyclic diolefins (particularlycyclopentadiene).

(2) Fractionation to distill C4C5 from Cs+ components of the heat soakedmixture.

(3) Superfractionation of C4-C5 distillate to remove heavy C5 components(piperylene concentrate) from isoprene and lighter components in thedistillate from step (2).

(4) Final fractionation to remove C4 and lighter C5 components from theisoprene concentrate, which is the distillate product from step (3).

The flow plan in the attached drawing illustrates a preferred method ofoperation.

In the drawing, a high temperature cracked naphtha fraction boiling inthe range of 30 F. to 420 F., but which contains a preponderance of C5and Cs unsaturated and aromatic hydrocarbons, serves as a startingmaterial from an initial zone 1. This feed material is passed by line 2into the heat soaking vessel 3.

In the heat soaking vessel 3, the naptha fraction is held attemperatures inthe range of 180 F. to 260 F. under a pressure of 120 p.s. i. g. for a number of hours until the cyclic diolefin components aredimerized. The cyclopentadiene, at its usual concentration in themixture, i. e. about .5 to 2 weight percent, will be 40 to 80% dimerizedat temperatures of 220 240 F. in about 8 to 12 hours.

The heat soaked naphtha fraction containing the formed dimers is passedfrom the soaker 3 by line 4 into an intermediate part of a fractionatingcolumn 5 to effect the separation between C5 and lighter components fromCs+ components with the use of moderate temperatures to minimizedimerization or polymerization of other dienes present and to minimizecracking of the dimers formed from the cyclic dienes.

Fractionating column 5 is equipped with a suitable number offractionating plates, e. g. about 20 to 30. Bottoms of Ce+ componentsare withdrawn by line 6. A portion of the bottoms is recycled throughreboiler 7. Distilled C5 and lighter components are withdrawn overheadthrough line 8. The overhead is condensed in condenser 9 and a portionis refluxed to the upper part of column 5 by line 10. The remainingportion of the distillate is passed on through line 11 by pump 12 intothe next fractionating column 13.

It has been found desirable to operate the first fractionating column 5at the lowest practical pressures, preferably about 0 to 30 p. s. i. g.This allows the use of low bottoms temperature, 190260 F., minimizingthe dimerization of cyclic dienes and also minimizing the cracking ofthe cyclic dienes formed in the heat soaking step. The overhead vaportemperatures that are suitable are in the range of F. to 170 F.

The intermediate fractionating column 13 is used as a superfractionatorto make a split between very closeboiling hydrocarbon components of thedistillate from column 5, i. e. to divide between isoprene and heaviercomponents which includes the piperylene. Column 13 is equipped with thenecessary fractionating plates, about 50 in number.

The residual liquid or bottom that is to include the piperylene iswithdrawn from the bottom part of column 13 by line 14, a portion ofthis bottom is recycled through the reboiler 15.

The distilled isoprene and lighter components are withdrawn overhead byline 16, and the vapors are condensed in condenser 17. A portion of thedistillate is refluxed by line 18 to the upper part of column 13.

By using proper conditions in the superfractionating column 13 asatisfactory separation may be made of iso prene from piperylene. It isadvantageous to use a somewhat higher pressure in column 13 than in thefirst fractionating column 5. In column 13, pressures of the order of1040 p. s. i. g. are suitable. Under this pressure the bottomstemperature is maintained at about 140 F.-190 F. and the overhead vaportemperature is kept at about F-170 F.

The overhead distillate from column 13 which is not refluxed is passedon by line 19 and pump 20 to an intermediate part of the thirdfractionating column 21 in which isoprene concentrate is to be collectedas a bottoms prodllCt.

Fractionating column 21 is equipped with from 20 to 30 plates. Theisoprene concentrate is removed as a bottoms product by line 22 and aportion of this bottoms is recycled through reboiler 23. C4 and light C5components are distilled overhead through line 24 and condensed incondenser 25. A portion of the distillate is refluxed by line 26 to theupper part of column 21. The remaining C4 and light C5 components arewithdrawn through line 27.

In column 21 a pressure in the range of 30-60 p. s. i. g. is used. Underthese pressures, the bottoms temperature of column 21 is maintained inthe range of 170 to 210 F. and the overhead vapor temperature ismaintained in the range of -160 F.

The normal procedure for a series of fractionating steps of this type isto remove progressively heavier overhead cuts. In this casefractionating columns 5, 13, and 21 are operated in such a manner as toremove progressively lighter bottoms cuts. This method of operation hasmany advantages in the preparation of isoprene and piperyleneconcentrates. By removing the Ce-lmaterial first at substantially lowpressures and temperatures, the fouling of equipment due to thepolymerization of dienes is minimized. As the pressure is increased inthe subsequent fractionating steps in columns 13 and 21, temperaturesbelow the level at which serious fouling occurs are possible since thereare no heavy ends present to raise the bottoms temperature. A furtheradvantage of this method of operation is that the circulation ofisoprene and piperylene through the tower reboilers is minimized. Thistends to reduce fouling, and it also increases the recovery of thesematerials by minimizing the formation of isoprene and piperylene dimersand codimers.

The bottoms from the superfiractionator column 13 is a piperyleneconcentrate having valuable uses as such or may be more easily purifiedby extractive distillation. In the 3rd column 21 the isopreneconcentrate obtained as a bottoms product may contain of the order of 20to 40 weight percent of isoprene well suited for extractivedistillation; for example, using aqueous acetone or other polar solventslike those that are known.

Procedures for purifying the isoprene and piperylene in their respectiveconcentrates by extractive distillation with aqueous acetone or otherpolar organic solvents are in the U. S. Patents 2,426,705, 2,426,706 ofPatterson et al. and John A. Patterson. These patents indicate thatthere are problems in making a separation between the various C5hydrocarbons and show that it has been diflicult to keep the isoprenefree of higher C5 components when the isoprene concentrate is distilledfrom a mixture which includes substantial amounts of cyclopentadiene andpiperylene.

With the method of the present invention the dimerization of the cyclicdiene and elimination of the cyclic diene as a drner should aid inbringing about a more clear cut separaton of isoprene from the higher C5component in which piperylene is retained.

Based on analyses of a representative feed composition, the followingfractionating column conditions and compositions of the product streamsobtainable are summarized:

TABLE Typical fractionating tower conditions for stream compositionsSplitter Super- Fraction- Tower Conditions Fraction- Fraetionator atorator Overhead Pressure, p. s. i. g -30 10-40 30-60 Overhead Temp, F100-170 110-170 130-160 Bottoms Temp., F 190-260 140-190 170-210Splitter Super- Fraction- Stream Compositions Fraction- Fractionatorator ator Component Feed OH Bot- OH Bot- OH Bottoms toms toms C4 2.0 4 725 Isoprene 7. 3 16 22 1 27 Piperylenm. 7. 3 15 1 1 41 1 Other C5S 29. 502 1 70 45 74 72 06+ 5 .9 3 98 9 The procedure of the present inventionallows recovery of an isoprene concentrate which contains substantiallyabove 20 weight percent isoprene with very little piperylene as comparedto the method wherein the isoprene concentrate is distilled from amixture containing the C5 components including cyclopentadiene and C5+components. For instance, as shown in U. S. Patent 2,426,705 theisoprene concentrate separated by the latter method did not very easilycontain as much as 20 weight percent or more of isoprene and would tendto be contaminated by more than 0.5 weight percent cyclopentadiene.

Although the present method does not require the presence of substantialamounts of C4 components in the initial feed, it can advantageouslytreat a feed which contains a substantial amount of C4 components.

The described invention is claimed as follows:

1. A process for separating isoprene and piperylene concentrates from anaphtha fraction containing mainly C4 to C12 alkenes, aromatichydrocarbons, and dienes, which comprises heat soaking under pressure attemperatures of about 180 to 260 F. for a number of hours to formdi-rners selectively from cyclic dienes therein, fractionally distillingC4 and C5 components from the heat soaked fraction at about 190 to 260F. under a pressure of 0 to 30 p. s. i. g. while keeping Cs+ componentsin the residual part of the heat soaked fraction, increasing pressure ofthe distilled C4 and C5 components, distilling isoprene and lighter C5components with C4 components from heavier C5 components containingpiperylene under increased pressure in the range of 10 to 20 p. s. i. g.at about to 190 F. further increasing pressure for the distilledisoprene and lighter components, and distilling C4 and C5 componentslighter than isoprene from a remaining portion of C componentscontaining the isoprene under an increased pressure of 30 to 60 p. s. i.g. at about to 210 F.

2. A process for separating isoprene and piperylene concentrates from anaphtha fraction containing mainly alkenes, aromatic hydrocarbons, anddienes in the C4 and C12 range, which comprises heat soaking saidfraction to selectively dimerize cyclic diene components in saidfraction at 180 to 260 F., fractionally distilling C4 and C5 componentsfrom the heat soaked fraction heated to a temperature of to 260 F. in afirst fractionation zone under a pressure of 0 to 30 p. s. i. g. whilekeeping Ce+ components with dimers of the cyclic dienes in a residualpart of said fraction, passing the C4 and C5 components distilled into ahigher pressure second fractionation zone under a pressure of 10 to 40p. s. i. g., and distitling from said second zone, isoprene with lighterC5 and C4 components while keeping piperylene in a part of the C5components heated to a temperature of 140 to 190 F.

3. A process for separating isoprene and piperylene concentrates from anaphtha fraction containing a preponderance of C5 and Cs unsaturated andaromatic hydrocarbons boiling in the range of 30 F. to 420 F., saidnaphtha fraction containing about 0.5 to 2 weight percentcyclopentadiene with isoprene and piperylene, which comprises heatsoaking said fraction to a selectively dimerized cyclic diene componenttherein at 180 to 260 F., fractionally distilling C4 and C5 componentsfrom the heat soaked fraction in a first fractionation zone under apressure of 0 to 30 p. s. i. g. with a bottoms temperature of 190 to 260F. while keeping aromatic Ce+ components with dimers of the cyclodienesin a bottoms part of said first fractionation zone, passing the C4 andC5 component into a higher pressure second fractionation zone,distilling isoprene with lighter C5 and C4 components under a pressureof 10 to 40 p. s. i. g. with a bottoms temperature of 140 to 190 F. insaid second Zone, passing the isoprene with the lighter C5 and C4components into a higher pressure third fractionation zone, anddistilling the C4 and C5 components lighter than isoprene overhead fromsaid third fractionation Zone under a pressure of 30 to 60 p. s. i. g.with a bottoms temperature of 170 to 210 F. to concentrate the isoprenein bottoms of the third fractionation Zone.

References Cited in the file of this patent UNITED STATES PATENTS

1. A PROCESS FOR SEPARATING ISOPRENE AND PIPERYLENE CONCENTRATES FROM ANAPHTHA FRACTION CONTAINING MAINLY C4 TO C12 ALKENES, AROMATICHYDROCARBONS, AND DIENES, WHICH COMPRISES HEAT SOAKING UNDER PRESSURE ATTEMPERATURES OF ABOUT 180* TO 260* F. FOR A NUMBER OF HOURS TO FORMDIMERS SELECTIVELY FROM CYCLIC DIENES THEREIN, FRACTIONALLY DISTILLINGC4 AND C5 COMPONENTS FROM THE HEAT SOAKED FRACTION AT ABOUT 190* TO 260*F. UNDER A PRESSURE OF 0 TO 30 P.S.I.G WHILE KEEPING C6+ COMPONENTS INTHE RESIDUAL PART OF THE HEAT SOAKED FRACTION, INCREASING PRESSURE OFTHE DISTILLED C4 AND C5 CONPONENTS, DISTILLING ISOPRENE AND LIGHTER C5COMPONENTS WITH C4 COMPONENTS FROM HEAVIER C5 COMPONENTS CONTAININGPIPERYLENE UNDER INCREASED PRESSURE IN THE RANGE OF 10 TO 20 P.S.I.G. ATABOUT 140* TO 190* F. FURTHER INCREASING PRESSURE FOR THE DISTILLEDISOPRENE AND LIGHTER COMPONENTS, AND DISTILLING C4 AND C5 COMPONENTSLIGHTER THAN ISOPRENE FROM A REMAINING PORTION OF C5 COMPONENTSCONTAINING THE ISOPRENE UNDER AN INCREASED PRESSURE OF 30 TO 60 P. S. I.G AT ABOUT 170* TO 210* F.